Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$225.47	7.469%	$242.3104	$242.31	$242.30	$242.30
Purchase #2	$162.80	5.653%	$172.0031	$172.00	$172.00	$172.00
Purchase #3	$53.31	3.858%	$55.3667	$55.37	$55.35	$55.40
Purchase #4	$51.33	6.305%	$54.5664	$54.57	$54.55	$54.60
Purchase #5	$172.90	10.144%	$190.439	$190.44	$190.45	$190.40
Purchase #6	$35.30	9.204%	$38.549	$38.55	$38.55	$38.50
Purchase #7	$141.48	11.718%	$158.0586	$158.06	$158.05	$158.10
7 purchase totals =	$842.59		$911.2932	$911.30	$911.25	$911.30